Finally after too many preview version, Apple has officially given iOS 9 update to its compatible iDevices. iOS 9 will be available to iPad 2, iPad 3, iPad 3 Mini, iPhone 5, 5S, 4S and 5th or 4th generation iPods. If you haven't received the update notification of iOS 9 yet, then Go to Setting -> General -> Tap on software update to start installing update.

iOS 9 requires a download of 1.3GB of ipa file. This will download easily if you device has just 16GB of storage.
There are many that you can find the iOS 9 like multi window, live photos, updated siri, etc.
Interesting new application is Wallet, that lets you store credit cards or reward cards to avail in Apple App store whenever required. See below the detailed updates you can find in iOS 9 and also please give your feedback via comments.

Apple iOS 9 - What's New

With this update your iPhone, iPad and iPod touch become more intelligent and proactive with powerful search and improved Siri features. New multitasking features for iPad allow you to work with two apps simultaneously, side-by-side or with the new Picture-in-Picture feature. And, built-in apps become more powerful with detailed transit information in Maps, a redesigned Notes app, and an all-new News app. And improvements at the foundation of the operating system enhance performance, improve security and give you up to an hour of extra battery life.Intelligence

Proactive assistance

Presents relevant information even before you start typing

Notifies you when you need to leave for appointments using traffic conditions

Learns what you listen to in a certain location or at a particular time of day and can automatically display playback controls for your preferred music and audio apps

Suggested events and contact details are added to apps based on information found in Mail

Siri improvements

Search your personal photos and videos based on dates, locations and album names

Ask Siri to remind you about things you’re looking at in your apps, including Safari, Mail, Notes and Messages

Expanded Per App VPN support for the built-in IPSec and IKEv2 VPN clients

New networking controls for managed apps to help limit international data roaming costs

New restrictions to prevent changes to passcodes, device names and wallpapers, or to disable AirDrop on managed devices

Third party app extension support for VPN, advanced content filtering, and captive Wi-Fi networks

Accessibility

Touch Accommodations provides additional touch control for those with physical motor limitations

Switch Control Recipes to customize features or create your own

Support for Siri Voices for VoiceOver users

Additional customization of AssistiveTouch

Hardware keyboard support for Key Repeat, Slow Keys and Sticky Keys

Improved MFi hearing aid audio routing to choose where audio is played

Author : Shoeb Ahmad Fareed

Designation:Founder & CEOBio:A Technology Leninist who believes that success can only be achieved if one has a practical implementation knowledge. He is a Computer Science Engineer, a professional blogger and a debugger.